When black walnuts ripen in fall, their hulls soften and turn from green to yellow, and soon they will start falling from the trees. If possible, though, you should pick black walnuts from the tree as opposed to waiting for them to fall. Not only will you avoid competing with local squirrels, but you also will harvest a riper walnut. Black walnuts ripen over a period of four to six weeks. By the time they all fall to the ground, some of them are past their prime.
Pick the black walnuts or shake them out of the tree.
Hull the nuts as soon as you harvest them. If left to sit, the hulls will taint the nuts' flavor. There are a variety of ways to hull a black walnut. The easiest way is to stomp on them. Or, if you have a hammer handy, hold the nut between your fingers and hit the seam of the hull with your hammer.
Dump all of the hulled nuts into a bucket of water and rub them clean with your hands to remove any juice or debris. Toss any nuts that float to the top. The meat in these walnuts has failed to mature properly.
Dry the walnuts. Spread them (less than three nuts deep) out on a wire screen and leave them in a cool, well-ventilated spot that is out of direct sunlight. The black walnuts should dry out in 2 to 3 weeks. At the end of that time, break open a nut. If the kernel snaps crisply, the nuts are dry. If not, leave them for another week or so, then check them again.
Store any black walnuts that you do not plan to shell in a cloth bag or wire basket. Keep them in a well-ventilated area that remains around 60 degrees F with about 70 percent humidity (the nuts will spoil if kept too dry). Preserved this way, shelled walnuts will last for about one year.
Soak any walnuts that you intend to shell in hot water for anywhere between 2 and 24 hours before you crack them. By moistening the kernels, you will get larger pieces when you harvest them. Remove the nuts from the hot water and cover them with a moist towel until you are ready to crack them.
Crack the black walnuts open with a black walnut cracker. If you don't have one, hold a nut firmly between your fingers with the pointed end up. Then strike the point with a hammer until the shell cracks open (squeezing the nut in a machinist's vise works well, too).
Extract the black walnut's kernel from the shell with a nut pick.
Place the black walnut meat in a plastic bag. If stored in the freezer, they will last for 2 years. If stored in the refrigerator, they will last up to 9 months. If first baked at 215 degrees F for 15 minutes, then stored at room temperature, they will last 3 or 4 weeks.